(a) Field of the Invention
The present invention relates to a liquid crystal display.
(b) Description of the Related Art
Generally, a conventional liquid crystal display (LCD) comprises two substrates having electrodes and liquid crystal injected therebetween. Light transmittance is adjusted by controlling the intensity of voltage being applied to the electrodes.
Hereinafter, the conventional LCD is explained in detail with reference to the accompanying drawings.
FIGS. 1A and 1B are sectional views of a conventional twisted-nematic liquid crystal display (TN-LCD). The TN-LCD in FIG. 1A, comprises: transparent glass substrates 1 and 2 facing each other; a liquid crystal layer 7 inserted between the substrates 1 and 2; and electrodes 3 and 4 formed respectively on the inner surfaces of the transparent glass substrates 1 and 2; and two polarizing plates 5 and 6 attached to the outer surface of the glass substrates 1 and 2 respectively for polarizing the light.
The electrode 3 of the lower substrate 1 is a pixel electrode, and the electrode 4 of the upper substrate 2 is a common electrode, and dielectric anisotropy ∈ of the liquid crystal layer 7 is positive.
In the absence of electric field, the long axis of the liquid crystal molecules 8 of the liquid crystal layer 7 is in parallel with the substrates 1 and 2, and the liquid crystal molecules 8 are twisted spirally from one substrate to the other substrate.
When a power V is connected to the electrodes 3 and 4, and sufficient electric field is present in the liquid crystal layer 7 in the direction of the arrow as illustrated in FIG. 1B, the major axis of the liquid crystal molecules 8 is in parallel with the direction of the electric field. This type of TN-LCD unfortunately results in having a narrow viewing angle.
To remedy this problem, a new method, an in-plane switching liquid crystal display (IPS-LCD), has been proposed recently. FIGS. 2A and 2B are sectional views of a conventional IPS-LCD. The main difference between the TN-LCD and the IPS-LCD lies with the placement of the electrodes 3 and 4.
Unlike the TN-LCD, both electrodes 3 and 4 of the IPS-LCD are formed on the same substrate, either upper or lower, in parallel to each other. In FIGS. 2A and 2B, the electrodes 3 and 4 are formed on the lower substrate 1 as an example. The dielectric anisotropy ∈ of the liquid crystal layer 7 may be positive or negative. The other reference numerals of FIGS. 2A and 2B represent the same elements of FIGS. 1A and 1B.
In the absence of electric field, the long axis of the liquid crystal molecules 8 of the liquid crystal layer 7 is parallel with the two substrates 1 and 2, or has a predetermined angle with respect to the two electrodes 3 and 4.
When a power V is connected to the two electrodes 3 and 4, and sufficient electric field is applied, the generated electric field is substantially parallel with the substrates 1 and 2, and perpendicular to the electrodes 3 and 4. Accordingly, the long axis of the liquid crystal molecules 8 at the center of the liquid crystal layer 7 is parallel with the electric field.
On the other hand, the liquid crystal molecules 8, away from the center of the liquid crystal layer 7, has a spirally twisted substructure since the liquid crystal molecules 8 near the substrates 1 and 2 maintain their initial state due to the alignment force.
However, the IPS-LCD has undesirable effects of reduced contrast ratio due to light leakage in the dark state and the decreased response speed of the liquid crystal molecules.